In prescribing certain ophthalmic lenses, for example progressive power lenses, it is essential for the ophthalmic practitioner to locate the position of a patient's pupil with respect to a spectacle frame which will subsequently hold the lens.
Progressive power lenses have at least two corrective powers and a blend zone between the two power zones. Such lenses are described in the following U.S. Pat. Nos. 3,687,528; 3,785,724; 3,910,691; 3,950,082; 4,002,439; 4,055,379; 4,056,311 and 4,062,629. It is desirable to locate the pupil behind one of the power zones and not in front of or near one of the blend zones. For this reason, laboratories which manufacture ophthalmic lenses ask the practitioner for pupil location relative to the bottom of a frame for which the progressive power lens is to be mounted. Presently, one method of locating the pupil is to take a spectacle frame and apply a piece of masking tape vertically over the front of the frame. The bottom of the frame is marked with a pencil and then the ophthalmic practitioner asks a patient to look at a distant object at eye level. When the patient does this, the ophthalmic practitioner makes another pencil mark on the masking tape at the elevation of the pupil. The practitioner then measures the distance between the two marks on the tape and submits this to the laboratory. One of the problems which is encountered is that the patient is made uncomfortable by the procedure. Moreover, since the tape is a stretchable and sticky material, inaccuracies result, as when the tape sticks to itself in an inchworm fashion. To avoid the inchworming effect, the tape may be stretched, but this causes inaccuracies in the opposite direction.
Horizontal pupillary distance, the distance between the line of sight of one eye and the line of sight of the other eye at a point in a near or far plane, may be measured by another technique. In one method, a narrow red strip is attached to each lens by means of a horizontal elastic member. For measurement of the near pupillary distance, the patient holds a red card with a green square. The red strip is moved across the lens until the patient sees the green square blocked with one eye open. The same is done with the other eye. The distance between the two strips is then measured by a ruler and is the measurement of the horizontal pupillary distance. This technique measures only the near interpupillary horizontal distance, not far, and has not been used to measure the pupil location vertically.
In U.S. Pat. No. 4,381,143, Bommarito discloses an ophthalmic test lens holder for use with spectacle frames by means of which test lenses may be inserted in the plane of said spectacles for measuring and testing purposes. A pair of elongated clamping members having at least one test lens holding bracket attached to one of the members are clamped over a pair of spectacle frames so that a test lens held by the bracket is positioned before a lens socket. Rulings on the clamping member are used to indicate distance and angles for the purpose of adjusting lenses with respect to a frame, for example the height of a bifocal line relative to the frame socket.
It is the object of the invention to devise a gauge for use with an ophthalmic test lens holder similar to the above type by means of which the measurement of the proper pupil position in relation to each power zone of a progressive lens is subjectively measured by the patient rather than objectively by the practitioner locating the pupil elevation while the patient looks at a distant or near object.
It is another object of the invention to devise a gauge which may be used with an ophthalmic lens holder, for measuring both horizontal pupillary distance and vertical pupil location to determine the visual axis.